OK, let's crack this. We're given 719 and our task is to multiply it by 21. Essentially, we'll be adding 719 to itself 21 times.
Step 1: 0 + 719 = 719
Step 2: 719 + 719 = 1438
Step 3: 1438 + 719 = 2157
Step 4: 2157 + 719 = 2876
Step 5: 2876 + 719 = 3595
Step 6: 3595 + 719 = 4314
Step 7: 4314 + 719 = 5033
Step 8: 5033 + 719 = 5752
Step 9: 5752 + 719 = 6471
Step 10: 6471 + 719 = 7190
Step 11: 7190 + 719 = 7909
Step 12: 7909 + 719 = 8628
Step 13: 8628 + 719 = 9347
Step 14: 9347 + 719 = 10066
Step 15: 10066 + 719 = 10785
Step 16: 10785 + 719 = 11504
Step 17: 11504 + 719 = 12223
Step 18: 12223 + 719 = 12942
Step 19: 12942 + 719 = 13661
Step 20: 13661 + 719 = 14380
Step 21: 14380 + 719 = 15099

So, 719*21 = 15099